Gasification unit, gasification unit control device and method, and integrated gasification combined cycle

ABSTRACT

A gasification unit includes a gasifier configured to gasify a carbon-containing solid fuel; a pressure vessel housing the gasification furnace; a pressure holding section that is to be filled with a pressurizing gas and is provided between the gasifier and the pressure vessel; a pressurizing gas supply device configured to supply a pressurizing gas to the pressure holding section; pressure equalizing pipes by which the inside of the gasifier is communicated with the pressure holding section; a pressure difference detection and estimation device configured to detect or estimate a pressure difference between a first pressure on the gasifier side and a second pressure on the pressure holding section side; and a control device configured to control the pressurizing gas supply device such that the second pressure is higher than the first pressure based on a detection or estimation result of the pressure difference detection and estimation device.

FIELD

The present invention relates to a gasification unit that partially combusts carbonaceous feedstock such as coal and biomass and gasifies them to generate gas fuel, a control device and a control method which control the gasification unit, and an integrated gasification combined cycle including the gasification unit.

BACKGROUND

An integrated gasification combined cycle (an integrated coal gasification combined cycle) includes a coal feeder, a coal gasification unit, a gas purification unit, a gas turbine unit, a steam turbine unit, a heat recovery steam generator, and a gas cleaner. The coal gasification unit in this integrated coal gasification combined cycle is configured by arranging a gasifier in a pressure vessel, arranging a combustion device in a vertically lower part of this gasifier, and arranging a heat exchanger (a gas cooler) in a vertically upper part thereof. The coal gasification unit fills an annulus section (a pressure holding section) between the pressure vessel and the gasifier with an inactive gas such as nitrogen to maintain the inside of the gasifier at a high-pressure state. The inside of the gasifier and the annulus section communicate with each other via pressure equalizing pipes to prevent the differential pressure between the inside of the gasifier and the annulus section caused by pressure fluctuations in the gasifier from rising. Examples of such a coal gasification unit include those described in the following Patent Literature 1 and 2.

CITATION LIST Patent Literature

Patent Literature 1: Japanese Patent Application Laid-open No. H07-278574

Patent Literature 2: Japanese Patent Application Laid-open No. 2013-163760

SUMMARY Technical Problem

In a coal gasification unit, when the supply amount of a fuel fluctuates during a load increase, and the pressure in a gasifier rises, a raw syngas in the gasifier flows into an annulus section through pressure equalizing pipes to prevent the differential pressure between the inside of the gasifier and the annulus section from rising. A pressurizing gas by an inactive gas such as nitrogen is supplied in order to maintain the pressure in the annulus section, whereby the raw syngas that has flowed from the gasifier into the annulus section is returned to the gasifier, and therefore the annulus section can maintain an inactive gas atmosphere. This raw syngas contains unreacted contents and ash contents (hereinafter, referred to as char), and this char nay flow into the annulus section together with the raw syngas. The coal gasification unit is provided with a slug bath that stores therein water in the lower end thereof, and the char that has flowed into the annulus section may contaminate the annulus section.

The present invention solves the above problem, and an object thereof is to provide a gasification unit, a device and method for controlling the gasification unit, and an integrated gasification combined cycle that can prevent the raw syngas from flowing into the annulus section (the pressure holding section) through the pressure equalizing pipes due to the pressure fluctuations in the gasifier.

Solution to Problem

To achieve the object, a gasification unit of the present invention includes a gasifier configured to gasify carbonaceous feedstock; a pressure vessel housing the gasifier; a pressure holding section to be filled with a pressurizing gas, the pressure holding section being provided between the gasifier and the pressure vessel; a pressurizing gas supply device configured to supply a pressurizing gas to the pressure holding section; pressure equalizing pipes by which the inside of the gasifier is communicated with the pressure holding section; a pressure difference detection and estimation device configured to detect or estimate a first pressure difference between a first pressure on the gasifier side and a second pressure on the pressure holding section side; and a control device configured to control the pressurizing gas supply device such that the second pressure is higher than the first pressure based on a detection result or an estimation result of the pressure difference detection and estimation device.

Consequently, the pressure vessel houses the gasifier, the pressure holding section is defined therebetween, the inside of the gasifier and the pressure holding section communicate with each other via the pressure equalizing pipes, and the pressurizing gas supply device supplies the pressurizing gas to the pressure holding section, thereby preventing a raw syngas from flowing from the gasifier into the pressure holding section. However, pressure fluctuations in the gasifier may raise the pressure in the gasifier, which may exceed the pressure in the pressure holding section. The pressure difference detection and estimation device detects or estimates the first pressure difference between the first pressure on the gasifier side end the second pressure on the pressure holding section side. The control device controls the pressurizing gas supply device such that the second pressure becomes higher than the first pressure based on the detection result or the estimation result of the pressure difference detection and estimation device. Consequently, even when the pressure in the gasifier rises, the pressure in the pressure holding section is raised more than it, whereby the raw syngas in the gasifier can be prevented from flowing into the pressure holding section through the pressure equalizing pipes.

In the gasification unit of the present invention, the pressure difference detection and estimation device includes a first pressure sensor provided apart from the pressure equalizing pipes in a gas flow direction to detect the first pressure in the gasifier, a second pressure sensor provided apart from the pressure equalizing pipes in the gas flow direction to detect the second pressure in the pressure holding section, and a calculator configured to calculate the first pressure difference from a detection value of the first pressure sensor and a detection value of the second pressure sensor.

Consequently, the first pressure sensor and the second pressure sensor that are provided apart from the pressure equalizing pipes are used, whereby the first pressure difference can be easily calculated. When the density of the raw syngas in the gasifier and the density of the pressurizing gas in the pressure holding section are different from each other, the pressure difference becomes larger toward a lower part. In order to ensure the furnace wall strength of the gasifier, the differential pressure between the inside of the gasifier and the pressure holding section is monitored using the first pressure sensor and the second pressure sensor that are provided apart from the pressure equalizing pipes. The differential pressure between the inside of the gasifier and the pressure holding section is detected using the first pressure sensor and the second pressure sensor, whereby the first pressure difference can be easily detected.

In the gasification unit of the present invention, the pressure difference detection and estimation device detects or estimates a second pressure difference between a third pressure on an opening of the pressure equalizing pipe on the gasifier side and a fourth pressure on an opening of the pressure equalizing pipe on the pressure holding section side, and the control device controls the pressurizing gas supply device such that the fourth pressure is higher than the third pressure based on a detection result or an estimation result of the pressure difference detection and estimation device.

Consequently, the third pressure on the opening of the pressure equalizing pipes on the gasifier side and the fourth pressure on the opening of the pressure equalizing pipes on the pressure holding section side are used, whereby the second pressure difference can be detected or estimated with high precision, and therefore the raw syngas in the gasifier can be prevented from flowing into the pressure holding section through the pressure equalizing pipes.

In the gasification unit of the present invention, a heat exchanger is arranged in a vertically upper part of the gasifier, the pressure equalizing pipes are arranged vertically above the heat exchanger, the pressure difference detection and estimation device includes a third pressure sensor configured to detect the third pressure, a fourth pressure sensor configured to detect the fourth pressure, and a calculator configured to calculate the second pressure difference from a detection value of the third pressure sensor and a detection value of the fourth pressure sensor, and the control device controls the pressurizing gas supply device such that the second pressure difference is a lover limit value with a tolerance set in advance added or more.

Consequently, the calculator calculates the second pressure difference from the detection value of the third pressure sensor and the detection value of the fourth pressure sensor, and the control device adjusts the supply amount of the pressurising gas to the pressure holding section by the pressurizing gas supply device such that the second pressure difference is the lower limit value or more. Thus, by directly detecting the pressure near the pressure equalizing pipes in the upper part of the gasifier by the sensors to determine the first pressure difference, the supply amount of the pressurizing gas to the pressure holding section can be adjusted with high precision.

In the gasification unit of the present invention, a supply amount of the pressurizing gas is controlled as the sum of a standard supply amount and a fluctuating supply amount, the standard supply amount being set such that the first pressure difference is a certain pressure difference or more, the certain pressure difference providing a pressure difference at a normal situation during normal rated operation, and the control device calculates the fluctuating supply amount to be additionally supplied at a pressure rising rate of the second pressure detected by the second pressure sensor in the pressure holding section.

Consequently, the supply amount of the pressurizing gas is the sum of the standard supply amount during rated operation and the fluctuating supply amount additionally supplied, whereby the pressure in the pressure holding section can be easily maintained higher than the pressure in the gasifier. In addition, the fluctuating supply amount at the rising rate of the second pressure near the pressure equalizing pipes is calculated, whereby the pressure in the pressure holding section can be maintained higher than the pressure in the gasifier with higher precision, a gas flow from the inside of the gasifier to the pressure holding section can be prevented appropriately, and thus the pressure holding section can be prevented from being contaminated.

In the gasification unit of the present invention, the first pressure sensor and the second pressure sensor are arranged at the same height position.

Consequently, even when the density of the raw syngas in the gasifier and the density of the pressurizing gas in the pressure holding section are different from each other, the first pressure sensor and the second pressure sensor, which are arranged at the same height position, detect the pressure in the gasifier and the pressure in the pressure holding section, respectively, and thus the supply amount of the pressurizing gas to the pressure holding section can be adjusted with high precision with detection errors reduced.

In the gasification unit of the present invention, a supply position of the pressurizing gas to the pressure holding section by the pressurizing gas supply device is a position apart from the pressure equalizing pipes vertically downward by a certain distance.

Consequently, the supply position of the pressurizing gas to the pressure holding section is provided at the position apart from the pressure equalizing pipes, lower than the pressure equalizing pipes, whereby the pressurizing gas flows upward to the pressure equalizing pipes in the pressure holding section, and even when foreign objects in the gasifier move to the pressure holding section through the pressure equalizing pipes, the foreign objects can be floated and discharged through the upward flow of the pressurizing gas.

In the gasification unit of the present invention, the pressure difference detection and estimation device includes a first pressure sensor provided apart from the pressure equalizing pipes in a gas flow direction to detect a first pressure in the gasifier, a second pressure sensor provided apart from the pressure equalizing pipes in the gas flow direction to detect a second pressure in the pressure holding section, and a calculator configured to calculate a second pressure difference from a detection value of the first pressure sensor and a detection value of the second pressure sensor, and the control device controls the pressurizing gas supply device such that the second pressure difference is an upper limit value set based on a furnace wall strength of the gasifier or less.

Consequently, the calculator calculates the second pressure difference from the first pressure detected by the first pressure sensor and the second pressure detected by the second pressure sensor, and the control device adjusts the supply amount of the pressurizing gas to the pressure holding section by the pressurizing gas supply device such that the second pressure difference is the upper limit value or less. When the density of the raw syngas in the gasifier and the density of the pressurizing gas in the pressure holding section are different from each other, the pressure difference becomes larger toward a lower part, and the upper limit value is set based on the furnace wall strength of the gasifier. Consequently, the supply amount of the pressurizing gas to the pressure holding section is adjusted in accordance with the second pressure difference in the lower part of the gasifier, whereby the raw syngas can be prevented from flowing into the pressure holding section, and the high integrity of the gasifier can be ensured.

In the gasification unit of the present invention, the pressure difference detection and estimation device includes a first pressure sensor configured to detect a first pressure, a second pressure sensor configured to detect a second pressure in a lower part of the pressure holding section, and an estimator configured to estimate the second pressure difference from a detection value of the first pressure sensor, a detection value of the second pressure sensor, and a height position of the pressure equalizing pipes, and the control device controls the pressurizing gas supply device such that the second pressure difference is maintained within a certain range set in advance.

Consequently, the estimator estimates the second pressure difference from the first pressure detected by the first pressure sensor, the second pressure detected by the second pressure sensor, and the height position of the pressure equalizing pipes, and the control device adjusts the supply amount of the pressurizing gas to the pressure holding section by the pressurizing gas supply device such that the second pressure difference is maintained within the certain range. Consequently, the first pressure difference is determined using the sensors for maintaining the strength of the gasifier without separately providing any sensor for detecting the pressure near the pressure equalizing pipes in the upper part of the gasifier, whereby the supply amount of the pressurizing gas to the pressure holding section can be appropriately adjusted, and parts costs can be prevented from increasing.

In the gasification unit of the present invention, the pressure difference detection and estimation device includes a fuel flow sensor configured to detect a fuel flow to be supplied to the gasifier and an estimator configured to estimate a pressure in the gasifier based on a detection value of the fuel flow sensor to estimate the first pressure difference, and the control device controls the pressurizing gas supply device such that the first pressure difference is maintained within a certain range set in advance.

Consequently, the estimator estimates the first pressure difference based on the fuel flow to be supplied to the gasifier detected by the fuel flow sensor, and the control device adjusts the supply amount of the pressurizing gas to the pressure holding section by the pressurizing gas supply device such that the first pressure difference is maintained within the certain range. Consequently, the first pressure difference is determined using the sensor for detecting the fuel flow to be supplied to the gasifier without separately providing any sensor for detecting the pressure near the pressure equalizing pipes in the upper part of the gasifier, whereby the supply amount of the pressurizing gas to the pressure holding section can be appropriately adjusted, and parts costs can be prevented from increasing.

In the gasification unit of the present invention, the pressure difference detection and estimation device includes a pressure sensor configured to detect a pressure in the gasifier and an estimator configured to calculate a furnace pressure rising rate of the gasifier based on a detection value of the pressure sensor to estimate the first pressure difference, and the control device controls the pressurizing gas supply device such that the first pressure difference is maintained within a certain range set in advance.

Consequently, the estimator estimates the first pressure difference based on the pressure in the gasifier detected by the pressure sensor, and the control device adjusts the supply amount of the pressurising gas to the pressure holding section by the pressurizing gas supply device such that the first pressure difference is maintained within the certain range. Consequently, the first pressure difference is determined using the sensor for detecting the pressure in the gasifier without separately providing any sensor for detecting the pressure near the pressure equalizing pipes in the upper part of the gasifier, whereby the supply amount of the pressurizing gas to the pressure holding section can be appropriately adjusted, and parts costs can be prevented from increasing.

In the gasification unit of the present invention, the pressure difference detection and estimation device includes a calculator configured to calculate the first pressure difference in accordance with a load change of the gasifier at start-up set in advance, and the control device controls the pressurizing gas supply device such that the first pressure difference is maintained within a certain range set in advance.

Consequently, the calculator calculates the first pressure difference in accordance with a load increase in the gasifier at start-up, and the control device adjusts the supply amount of the pressurizing gas to the pressure holding section by the pressurizing gas supply device such that the first pressure difference is maintained within the certain range Consequently, the supply amount of the pressurizing gas can be sot without using any pressure sensor, fluctuations in the supply amount of the pressurizing gas caused by detection errors and detection delays can be reduced, and the supply amount of the pressurizing gas to the pressure holding section can be adjusted with high precision.

A control device of the present invention is for a gasification unit that includes a gasifier configured to gasify a carbon-containing fuel, a pressure vessel housing the gasifier, a pressure holding section to be filled with a pressurizing gas, the pressure holding section being provided between the gasifier and the pressure vessel, a pressurizing gas supply device configured to supply a pressurizing gas to the pressure holding section, and pressure equalizing pipes by which the inside of the gasifier is communicated with the pressure holding section. The control device controls the pressurizing gas supply device such that a second pressure on the pressure holding section side is higher than a first pressure on the gasifier side.

Consequently, the pressurizing gas supply device is controlled such that the second pressure is higher than the first pressure based on the detection result or the estimation result of the pressure difference detection and estimation device, and therefore even when the pressure in the gasifier rises, the pressure in the pressure holding section is raised more than it, whereby the raw syngas in the gasifier can be prevented from flowing into the pressure holding section through the pressure equalizing pipes.

A control method of the present invention is for a gasification unit that includes a gasifier configured to gasify a carbon-containing fuel, a pressure vessel housing the gasifier, a pressure holding section to be filled with a pressurizing gas, the pressure holding section being provided between the gasifier and the pressure vessel, a pressurizing gas supply device configured to supply a pressurizing gas to the pressure holding section, and pressure equalizing pipes by which the inside of the gasifier is communicated with the pressure holding section. The control method includes detecting or estimating a first pressure difference between a first pressure on the gasifier side and a second pressure on the pressure holding section side; and controlling the pressurizing gas supply device such that the second pressure is higher than the first pressure.

Consequently, even when the pressure in the gasifier rises, the pressure in the pressure holding section is raised more than it, whereby the raw syngas in the gasifier can be prevented from flowing into the pressure holding section through the pressure equalizing pipes.

An integrated gasification combined cycle of the present invention includes the gasification unit configured to gasify carbonaceous feedstock to generate a combustible gas; a gas purification unit configured to remove impurities from the combustible gas generated by the gasification unit to perform gas purification; a gas turbine unit configured to combust a mixed gas of at least part of the combustible gas subjected to gas purification by the gas purification unit and compressed air to rotatingly drive a turbine; a heat recovery steam generator configured to generate steam by a flue gas from the gas turbine unit; and a steam turbine unit configured to rotatingly drive a turbine by the steam generated by the heat recovery steam generator.

Consequently, the gasification unit controls the pressurizing gas supply device such that the second pressure is higher than the first pressure based on the detection result or the estimation result of the pressure difference detection and estimation device, and therefore even when the pressure in the gasifier rises, the pressure in the pressure holding section is raised more than it, whereby the raw syngas in the gasifier can be prevented from flowing into the pressure holding section through the pressure equalizing pipes. Consequently, char is prevented from dropping in the pressure holding section, and the annulus section can be prevented from being contaminated.

Advantageous Effects of Invention

The gasification unit, the device and method for controlling the gasification unit, and the integrated gasification combined cycle of the present invention control the pressurizing gas supply device such that the second pressure on the opening on the pressure holding section side is higher than the first pressure on the opening on the gasifier side of the pressure equalizing pipes which is to counteract pressure fluctuations in the gasifier and can thus prevent the raw syngas in the gasifier from flowing into the pressure holding section through the pressure equalizing pipes.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic diagram illustrating a gasification unit of a first embodiment.

FIG. 2 is a schematic block diagram of an integrated coal gasification combined cycle in which the gasification unit of the first embodiment is used.

FIG. 3 is a schematic diagram illustrating a gasification unit of a second embodiment.

FIG. 4 is a schematic diagram illustrating a gasification unit of a third embodiment.

FIG. 5 is a schematic diagram illustrating a gasification unit of a fourth embodiment.

DESCRIPTION OF EMBODIMENTS

The following describes preferred embodiments of a gasification unit, a device and method for controlling the gasification unit, and an integrated gasification combined cycle according to the present invention in detail with reference to the accompanying drawings. The present invention is not limited to the embodiments and, if there are a plurality of embodiments, also includes a combination of the embodiments.

First Embodiment

FIG. 2 is a schematic block diagram of an integrated coal gasification combined cycle in which a gasification unit of a first embodiment is used.

An integrated coal gasification combined cycle (IGCC) facility of the first embodiment employs an air combustion system that generates a coal gas by a gasification unit with air as an oxygen containing gas and supplies the coal gas after being purified by a gas purification unit to a gas turbine unit as a fuel gas to perform power generation. In other words, the integrated coal gasification combined cycle of the first embodiment is an air combustion type (air blown) power generation plant. Examples of a fuel to be supplied to the gasification unit include carbonaceous feedstock such as coal.

In the first embodiment, as illustrated in FIG. 2, the integrated coal gasification combined cycle (the integrated gasification combined cycle) 10 includes a powdered coal supply unit 11, a coal gasification unit 12, a char recovery unit 13, a gas purification unit 14, a combined cycle power unit 15, and a heat recovery steam generator (HRSG) 16.

The powdered coal supply unit 11 is a plant that pulverizes coal into fine particles to manufacture powdered coal. The powdered coal manufactured by the powdered coal supply unit is supplied to the coal gasification unit 12. The coal gasification unit 12 is a device that uses the powdered coal and can use char (unreacted coal and ash content) recovered by the char recovery unit 13. The coal gasification unit 12 partially combusts the coal (the powdered coal) as a carbon-containing fuel supplied to the inside thereof with an oxygen containing gas (air and oxygen) to gasify it and generates a combustible gas. This coal gasification unit 12 is provided with a gas generation line 31 for the combustible gas toward the char recovery unit 13 and can discharge the combustible gas containing char.

The char recovery unit 13 has a precipitator and a supply hopper, in this case, the precipitator includes one or more porous filters or cyclones; the char contained in the combustible gas generated by the coal gasification unit 12 can be separated. The combustible gas from which the char has been separated is sent to the gas purification unit 14 through a gas discharge line 32.

The gas purification unit 14 removes impurities such as sulfur compounds and nitrogen compounds from the combustible gas from which the char has been separated by the char recovery unit 13 to perform gas purification. The gas purification unit 14 purifies the combustible gas to manufacture a fuel gas and supplies it to the combined cycle power unit 15.

The combined cycle power unit 15 includes a gas turbine unit, a steam turbine unit, and a generator. The heat recovery steam generator 16 generates steam by the heat of an exhaust gas used in the steam turbine unit of the combined cycle power unit 25 and sends it to the steam turbine unit. Toxic substances in the flue gas from which the heat has been recovered by the heat recovery steam generator 16 are removed by a gas cleaner 33, and the cleaned flue gas is discharged to the atmosphere from a stack 34.

In the thus configured integrated coal gasification combined cycle 10, the powdered coal generated by the powdered coal supply unit 11 is supplied to the coal gasification unit 12. The char recovered by the char recovery unit 13 is supplied to the coal gasification unit 12. The coal gasification unit 12 combusts the supplied powdered coal and char with compressed air (oxygen) to gasify the powdered coal and char, thereby generating the combustible gas (a coal gas). This combustible gas is discharged from the coal gasification unit 12 through the gas generation line 31 and is sent to the char recovery unit 13. In the char recovery unit 13, the char is separated from the combustible gas by the precipitator, and the combustible gas from which the char has been separated is sent to the gas purification unit 14 through the gas discharge line 32. The powdered char that has been separated from the combustible gas is returned to the coal gasification unit 12 to be recycled.

The combustible gas from which the char has been separated is subjected to gas purification by removing impurities such as sulfur compounds and nitrogen compounds in the gas purification unit 14, and the fuel gas is manufactured. The combined cycle power unit 15 mixes compressed air supplied from the gas turbine unit and the fuel gas supplied from the gas purification unit 14, combusts them, thereby generates a combustion gas to drive a turbine, and performs power generation by means of the generator. The exhaust gas discharged from the gas turbine unit undergoes water feeding and heat exchange in the heat recovery steam generator If to generated steam, and this generated steam is supplied to the steam turbine unit to rotatingly drive the turbine, whereby the generator performs power generation. The gas cleaner 33 removes the toxic substances of the exhaust gas discharged from the heat recovery steam generator 16, and the cleaned exhaust gas is discharged to the atmosphere from the stack 34.

The following describes the coal gasification unit 12 in the integrated coal gasification combined cycle 10 in detail. FIG. 1 is a schematic diagram illustrating the gasification unit of the first embodiment.

In the present embodiment, as illustrated in FIG. 1, the coal gasification unit 12 has a gasifier 101 that gasifies coal (powdered coal) as a carbonaceous feedstock, heat exchangers 102 arranged in the upper part of the gasifier 101, and a pressure vessel 103 that houses the gasifier 101; an annulus section (a pressure holding section) 104 is defined between the gasifier 101 and the pressure vessel 103.

The gasifier 101 has a hollow shape, in which a reductor 111, a diffuser 112, and a combustor 113 are provided from the upper part in the vertical direction. In this gasifier 101, a heat exchanger housing 114 that houses the heat exchangers 102 is provided vertically above the reductor 111, and a gas outlet 115 is formed above the heat exchanger housing 114. At least part of a furnace wall face of this gasifier 101 is formed by a plurality of heat transfer pipes (not illustrated) extending in the vertical direction of the furnace wall and arranged side by side in the circumferential direction.

The pressure vessel 103 has a hollow shape, in which an upper end in the vertical direction is connected to the outer circumferential part of the gasifier 101, and a slug bath 116 that stores therein water is provided at a lower end. The gasifier 101 is water-sealed by causing its lower end to be immersed in the stored water of the slug bath 116. This pressure vessel 103 arranges the gasifier 101 thereinside, thereby defining the annulus section 104 in a space between the gasifier 101 and the pressure vessel 103.

The combustor 113 is a space in which powdered coal, char, and air are partially combusted. A high-temperature combustion gas after combusting part of the powdered coal and char by the combustor 113 passes through the diffuser 112 to flow into the reductor 111. The reductor 111 is a space that is maintained at a high-temperature state required for a gasification reaction, supplies powdered coal to the combustion gas from the combustor 113, and thermally decomposes the powdered coal into volatile content (carbon monoxide, hydrogen, lower hydrocarbons, and the like), which is gasified and generated as a combustible gas; the gasified combustible gas (a raw syngas) flows from the lower part toward the upper part in the vertical direction.

The pressure vessel 103 is provided with a pressurizing gas supply device 119 that supplies an inert gas (an inert gas as an inactive gas, a carbon dioxide gas, and a natural gas, for example) as a pressurizing gas to the annulus section 104 formed between this pressure vessel 103 and the gasifier 101. In other words, a plurality of gas nozzles 120 are provided in the circumferential direction of the pressure vessel 103 end ere fixed such that they pass through this pressure vessel 103 to cause their tips to be positioned in the annulus section 104. These gas nozzles 120 are provided outside the redactor 111 in the pressure vessel 103, and an inert gas supply line 121 as the pressurizing gas is connected thereto. The inert gas supply line 121 is provided with a flow control valve 122. The inert gas is supplied to the lower part of the annulus section 104 through the gas nozzles 120, and this inert gas then ascends in the annulus section 104 to fill the entire region thereof.

The heat exchangers 102 are provided inside the wall face of the gasifier 101 and are provided vertically above the reductor 111. The heat exchangers 102 are provided in the vertically up-and-down direction and performs heat exchange with the raw syngas generated in the reductor 111 to cool the generate gas. The number of the heat exchangers 102 is not limited.

The gasifier 101 is provided with a plurality of pressure equalizing pipes 127, at certain intervals in the circumferential direction, which cause the upper part of the inside of the gasifier 101 and the upper part of the annulus section 104 to communicate with each other. The pressure equalizing pipes 127 each have an L shape, for example; one ends thereof communicate with the wall face of the gasifier 101 vertically above the heat exchangers 102, and the other ends thereof open downward in the annulus section 104. The supply positions of the inert gas to the annulus section 104 by the gas nozzles 120 of the pressurizing gas supply device 119 are set at positions apart from the pressure equalizing pipes 127 vertically downward by a certain distance. The “certain distance” is a distance that enables foreign objects to be floated and discharged through the upward flow of the inert gas.

The coal gasification unit 12 fills the annulus section 104 between the gasifier 101 and the pressure vessel 103 with the inert gas to maintain a high-pressure state within the gasifier 101 by the annulus section 104. The inside of the gasifier 101 and the annulus section 104 communicate with each other via the pressure equalizing pipes 127, thereby making the inside of the gasifier 101 and the outside thereof (the annulus section 104) the same pressure. The pressure equalizing pipes 127 prevent the differential pressure between the inside of the gasifier 101 and the annulus section 104 caused by pressure fluctuations in the gasifier 101 from rising.

However, when a fuel supply amount fluctuates during the load increase of the coal gasification unit 12, or when the fuel supply amount fluctuates even during rated operation, the pressure in the gasifier 101 rises, and if the pressure in the annulus section 104 does not change and remains lower than the pressure in the gasifier 101, the raw syngas in the gasifier 101 flows into the annulus section 104 through the pressure equalizing pipes 127. This raw syngas contains char, and this char flows into the annulus section 104 and may contaminate the annulus section 104.

Given this situation, the coal gasification unit 12 of the present embodiment constantly controls the supply amount of the inert gas to be supplied from the gas nozzles 120 to the annulus section 104 such that the pressure on the annulus section 104 side is higher than the pressure in the gasifier 101.

In other words, the coal gasification unit 12 is provided with a pressure difference detector 131 that detects a first pressure difference ΔP1 between a first pressure P1 inside the gasifier 101 of the reductor 111 and a second pressure P2 on the annulus section 104 side and a control device 132 that controls the pressurizing gas supply device 119 such that the second pressure P2 is higher than the first pressure P1 based on a detection result of the pressure difference detector 131.

The pressure difference detector 131 measures pressure in the reductor 111 of the gasifier 101 vertically below the heat exchangers 102. The pressure difference detector 131 has a first pressure sensor 136 that defect the first pressure P1, a second pressure sensor 137 that detects the second pressure P2, and a calculator 139 that calculates the first pressure difference ΔP1 from a detection value of the first pressure sensor 136 and a detection value of the second pressure sensor 137. In this case, the first pressure sensor 136 and the second pressure sensor 137 are arranged at the same height position. In other words, the first pressure sensor 136 is arranged inside the furnace wall of the gasifier 101, whereas the second pressure sensor 137 is arranged at a position radially opposite to the first pressure sensor 136 in the annulus section 104. The same height is not limited to exactly the same height; they may be arranged within a certain height range that causes no substantial difference in the measured pressure in consideration of a gas head difference present in the height direction including installation positions and installation errors.

To the calculator 136, the first pressure P1 detected by the first pressure sensor 136 and the second pressure P2 detected by the second pressure sensor 137 are input. The calculator 138 calculates the first pressure difference ΔP1 obtained by subtracting the first pressure P1 from the second pressure P2.

The control device 132 comperes the first pressure difference ΔP1 calculated by the calculator 138 with a lower limit value PL set in advance and determines whether the first pressure difference ΔP1 is the lower limit value PL or more. This lower limit value PL is a tolerance (allowed value) set based on design values or fluctuating values determined by an experiment or the like in advance. The control device 132 controls the pressurizing gas supply device 119 such that the first pressure difference ΔP1 is the lower limit value PL or more.

The supply amount of the inert gas by the pressurizing gas supply device 119 is supplied under constant control. The supply amount of the inert gas by the pressurizing gas supply device 119 is controlled as the sum of a standard supply amount and a fluctuating supply amount. The standard supply amount is set such that the first pressure difference ΔP1 is a certain pressure difference that is capable of producing a pressure difference at a normal situation during normal rated operation or more. The standard supply amount is set by the lever limit value PL (a tolerance set based on design values or fluctuating values determined by an experiment or the like in advance).

In other words, the standard supply amount is set based on the pressure in the annulus section 104, the volume of the annulus section 104, a holding inert gas amount in the annulus section 104, and the inert gas temperature of the annulus section 104. In this case, the pressure in the annulus section 104 and the inert gas temperature of the annulus section 104 are measured by sensors (not illustrated), whereas the volume of the annulus section 104 and the holding inert gas amount in the annulus section 104 are determined by design values. The inert gas in the standard supply amount is supplied by the control device 132, and the inert gas that has been introduced to the annulus section 104 flows from the annulus section 104 into the gasifier 101 through the pressure equalizing pipes 127 and is mixed with the raw syngas; the flow of the inert gas is sufficiently smaller than the flow of the raw syngas, and therefore there is no hindrance.

Next, when the first pressure difference ΔP1 changes by pressure fluctuations, an additional supply amount of the inert gas by the pressurizing gas supply device 119 is calculated. In other words, the pressure rising rate of the second pressure P2 by the second pressure sensor 137 in the annulus section 104 is calculated, and the control device 132 calculates the fluctuating supply amount to be additionally supplied because other shape and state remain unchanged. The control device 132 adds the fluctuating supply amount to be additionally supplied in response to pressure fluctuations to the standard supply amount of the inert gas calculated based on the lower limit value PL and supplies an appropriate supply amount of the inert gas as the sum of the standard supply amount and the fluctuating supply amount by the pressurizing gas supply device 119.

The control device 132 compares the first pressure difference ΔP1 calculated by the calculator 138 with an upper limit value PU set in advance and determines whether the first pressure difference ΔP1 is the upper limit value PU or less. This upper limit value PU is set in consideration of the strength of the furnace wall of the gasifier 101. In other words, in designing the furnace wall of the gasifier 101, an upper limit value for the pressure difference between the pressure in the gasifier 101 and that in the annulus section 104 is set, and the upper limit value of the pressure difference is the upper limit value PU. The control device 132 controls the pressurizing gas supply device 119 such that the first pressure difference ΔP1 is the upper limit value PU or less.

The upper limit value PU is set in accordance with the strength of the furnace wall of the gasifier 101 and monitors the first pressure difference ΔP1 between the pressure in the gasifier and that outside the gasifier (the annulus section) for the purpose of protecting the furnace wall of the reductor 111. The control device 132 increases the supply amount of the inert gas by the pressurizing gas supply device 119 to the extent that the first pressure difference ΔP1 is the upper limit value PU or less. When the inert gas is supplied to the annulus section 104 more than necessary, the inert gas's manufacturing costs increase, and an appropriate amount of the inert gas is desirably supplied to the annulus section 104.

The following describes modifications of the first embodiment.

First Modification

The following describes a method of control by a pressure difference with higher accuracy. The coal gasification unit 12 is further provided with the pressure difference detector 131 that detects a second pressure difference ΔP2 between a third pressure P3 on an opening 127 a of the pressure equalizing pipe 127 on the gasifier 101 side and a fourth pressure P4 on an opening 127 b of the pressure equalizing pipe 127 on the annulus section 104 side and the control device 132 that controls the pressurizing gas supply device 119 such that the fourth pressure P4 is higher than the third pressure P3 based on a detection result of the pressure difference detector 131.

In other words, the pressure difference detector 131 further measures the pressure in the annulus section 104 and the gasifier 101 of the pressure equalizing pipes 127. The pressure difference detector 131 has a third pressure sensor 133 that detects the third pressure P3 in the gasifier 101, a fourth pressure sensor 134 that detects the fourth pressure P4 in the annulus section 104, and a calculator 135 that calculates the second pressure difference ΔP2 from a detection value of the third pressure sensor 133 and a detection value of the fourth pressure sensor 134. In this case, the third pressure sensor 133 and the fourth pressure sensor 134 are arranged at the same height position. In other words, the third pressure sensor 133 is arranged at a position that is vertically below the opening on the gasifier 101 side of the pressure equalizing pipes 127 and is radially opposite thereto through the furnace wall of the gasifier 101. The fourth pressure sensor 134 is arranged at a position that is opposite to and vertically below the opening 127 b on the annulus section 104 side of the pressure equalizing pipes 127. The same height is not limited to exactly the same height; they may be arranged within a certain height range that causes no substantial difference in the measured pressure in consideration of a gas head difference present in the height direction including installation positions and installation errors.

To the calculator 135, the third pressure P3 detected by the third pressure sensor 133 and the fourth pressure P4 detected by the fourth pressure sensor 134 are input. The calculator 135 calculates the second pressure difference ΔP2 obtained by subtracting the third pressure P3 from the fourth pressure P4.

The raw syngas ascending vertically upward in the gasifier 101 and the inert gas ascending in the annulus section 104 are different in density. With this difference, the first pressure difference ΔP1 at the arrangement position of the first and second pressure sensors 136 and 137 and the second pressure difference ΔP2 at the arrangement position of the third and fourth pressure sensors 133 and 134 are different from each other by their heights, that is, in a gas head difference, and in actuality, the first pressure difference ΔP1 is larger than the second pressure difference ΔP2. In other words, the second pressure difference ΔP2 is smaller than the first pressure difference ΔP1, and the raw syngas in the gasifier 101 may flow into the annulus section 104 through the pressure equalizing pipes 127. For this reason, it is further preferable to monitor the second pressure difference ΔP2 to monitor and prevent the flow of the raw syngas into the annulus section 104 through the pressure equalizing pipes 127.

When the second pressure difference ΔP2 is increased in order to prevent the raw syngas from flowing into the annulus section 104 through the pressure equalizing pipes 127, the first pressure difference ΔP1 increases more than it, and the durability of the furnace wall of the gasifier 101 may become insufficient. For this reason, the upper limit value PU is set in accordance with the strength of the furnace wall of the gasifier 101. The control device 132 increases the supply amount of the inert gas by the pressurizing gas supply device 119 so as to be a sum obtained by adding the standard supply amount of the inert gas calculated based on the lower limit value PL and the fluctuating supply amount to be additionally supplied in response to pressure fluctuations to the extent that the first pressure difference ΔP1 is the upper limit value PU or less to supply an appropriate supply amount of the inert gas. This supply amount of the inert gas is controlled to a lower limit flow while controlling an upper limit flow, and the inert gas is prevented from being supplied to the annulus section 104 mere than necessary, the manufacturing costs of the inert gas are prevented from increasing, and an appropriate amount of the inert gas is supplied to the annulus section 104, which is thus desirable.

Second Modification

In many cases, the coal gasification unit 12 is operated to increase the load of the gasifier 101 from its start-up, to maintain a stationary load set in advance, to decrease the load of the gasifier 101, and to maintain a load set in advance. In this case, the coal gasification unit 12 increases a fuel flow to be supplied to the gasifier 101, in which a load rising rate at start-up, that is, the degree of increase of the fuel flow is set in advance. In contrast, a load reduction rate, that is, the degree of reduction of the fuel flow may be set in advance. Given these circumstances, the pressure difference detector 131 (the calculators 135 and 138) estimates and sets an estimated value of the first pressure difference ΔP1 or an estimated value of the second pressure difference ΔP2 in accordance with the load change of the gasifier 101 at start-up set in advance, whereby the control device 132 changes in advance the supply amount of the inert gas by the pressurizing gas supply device 119 so as to be the suss obtained by adding the standard supply amount of the inert gas calculated based on the lower limit value PL and the fluctuating flow amount to be additionally supplied based on the estimation of pressure fluctuations and supplies the inert gas in a supply amount estimated to be appropriate, with this operation, the control device controls the pressurizing gas supply device 119 such that the first pressure difference ΔP1 or the second pressure difference ΔP2 is maintained within a certain range set in advance, that is, between the lower limit value PL and the upper limit value PU.

The following describes the operation of the coal gasification unit 12 of the first embodiment, the first modification, and the second modification.

In the coal gasification unit 12, nitrogen and powdered coal are charged into the gasifier 101 and are ignited, and char and compressed air (oxygen) are charged thereinto and are ignited. Then, the combustion of the powdered coal and the char generates a high-temperature combustion gas in the combustor 113. The high-temperature combustion gas generated in the combustor 113 passes through the diffuser 112 and ascends to the redactor 111. In this reductor 111, the powdered coal is mixed with the high-temperature combustion gas, a gasification reaction is carried out in a high-temperature reducing atmosphere, and a combustible gas (a coal gas) is generated.

The pressurizing gas supply device 119 supplies the inert gas by the gas nozzles 120 to the annulus section 104 between the gasifier 101 and the pressure vessel 103, and this inert gas ascends vertically upward in the annulus section 104. The gasifier 101 and the annulus section 104 are provided with, in the upper part, the pressure equalizing pipes 127 through which the gasifier 101 and the annulus section 104 communicate with each other, and even when the pressure in the gasifier 101 fluctuates by the load fluctuations of the coal gasification unit 12 and the like, the pressure equalizing pipes 127 prevent the differential pressure between the gasifier 101 and the annulus section 104 frost rising.

In other words, in the coal gasification unit 12, the pressurizing gas supply device 119 supplies a certain inert gas to the annulus section 104 during operation, whereby the pressure in the annulus section 104 is maintained higher than the pressure in the gasifier 101. Owing to pressure fluctuations in the gasifier 101 and the like, the pressure of the raw syngas ascending in this gasifier 101 may become higher than the pressure in the annulus section 104. Then if the pressure in the annulus section 104 does not change to remain lower than the pressure in the gasifier 101, part of the raw syngas in the gasifier 101 flows into the annulus section 104 through the pressure equalizing pipes 127, and the char contained in this raw syngas may also flow into the annulus section 104.

Given these circumstances, in the pressure difference detector 131, the first pressure sensor 136 detects the first pressure P1, the second pressure sensor 137 detects the second pressure P2, and the calculator 138 calculates the first pressure difference ΔP1 between the first pressure P1 and the second pressure P2. Using the first pressure difference ΔP1 calculated by the calculator 138, the control device 132 controls the pressurizing gas supply device 119 such that an inert gas amount of the suss of the standard supply amount required for maintaining the lower limit value PL and the fluctuating supply amount calculated from the rising rate of the second pressure P2 is supplied. In other words, when the pressure of the raw syngas rises owing to pressure fluctuations in the gasifier 101 and the like, the supply amount of the inert gas to be supplied to the annulus section 104 by the pressurizing gas supply device 119 is increased, consequently, even when the pressure in the gasifier 101 increases, the pressure in the annulus section 104 also increases, and the pressure in the gasifier 101 does not exceed the pressure in the annulus section 104, and the raw syngas in the gasifier 101 can be prevented from flowing into the annulus section 104 through the pressure equalizing pipes 127.

In this case. If the first pressure difference ΔP1 is lower than the lower limit value PL, the control device 132 increases the supply amount of the inert gas to the annulus section 104, however, the first pressure difference ΔP1 is not required to be increased right before the upper limit value PU, and when the first pressure difference ΔP1 exceeds the lower limit value PL by a certain value, the increasing of the supply amount of the inert gas to the annulus section 104 may be stopped to maintain the supply amount.

Subsequently, when the coal gasification unit 12 returns to the rated operation, the pressure in the gasifier 101 drops. Then, the pressure in the annulus section 104 becomes significantly higher than the pressure in the gasifier 101, and the inert gas in the annulus section 104 flows into the gasifier 101 through the pressure equalizing pipes 127, which may idly consume the inert gas. Given this situation, there is a method for monitoring the pressure difference with higher precision as described in the second modification. In other words, in the pressure difference detector 131, the third pressure sensor 133 detects the third pressure P3 in the gasifier 101, the fourth pressure sensor 134 detects the fourth pressure P4 in the annulus section 104, and the calculator 135 calculates the second pressure difference ΔP2 between the third pressure P3 and the fourth pressure P4. Using the second pressure difference ΔP2 calculated by the calculator 135, the control device 132 controls the pressurizing gas supply device 119 such that the inert gas amount of the sum of the standard supply amount required for maintaining the lower value PL and the fluctuating supply amount calculated from the rising rate of the fourth pressure P4 is supplied. As to the second pressure difference ΔP2 compared with the first pressure difference ΔP1, gas head difference is obvious, and therefore the pressure difference between the front and rear of the pressure equalizing pipes 127 can be monitored with the value of the second pressure difference ΔP2, with higher precision rather than with the value of the first pressure difference ΔP1, and the raw syngas in the gasifier 101 can be prevented from flowing into the annulus section 104 through the pressure equalizing pipes 127, and thus it is further preferable to monitor the second pressure difference ΔP2.

As described in the second modification, there is a method that monitors the upper limit and the lower limit of the pressure difference, in other words, the upper limit is set such that the first pressure difference ΔP1 is the upper limit value PU or less in accordance with the strength of the furnace wall of the gasifier 101. The lower limit is set such that an appropriate supply amount of the inert gas is supplied by increasing the supply amount of the inert gas by the pressurizing gas supply device 119 so as to be the sum obtained by adding the standard supply amount of the inert gas calculated based on the lower limit value PL by the second pressure difference ΔP2 and the fluctuating supply amount additionally supplied by pressure fluctuations in order to prevent the raw syngas from flowing into the annulus section 104 through the pressure equalizing pipes 127. The supply amount of the inert gas is set within the range of the upper limit and the lower limit to be appropriately managed, and the manufacturing costs of the inert gas can be prevented from increasing, and an appropriate amount of the inert gas is supplied to the annulus section 104, which is thus desirable.

Thus, the gasification unit of the first embodiment includes the gasifier 101, the pressure vessel 103, the annulus section 104 filled with the inert gas between the gasifier 101 and the pressure vessel 103, the pressurizing gas supply device 119 that supplies the inert gas to the annulus section 104, the pressure equalizing pipes 127 that cause the inside of the gasifier 101 and the annulus section 104 to communicate with each other, the pressure difference detector 131 that detects the first pressure difference ΔP1 in the reductor 111, the pressure difference detector 131 that detects the second pressure difference ΔP2 in the pressure equalizing pipes 127, and the control device 132 that controls the pressurizing gas supply device 119 such that the raw syngas is prevented from flowing into the annulus section 104 through the pressure equalizing pipes 127 using the first pressure difference ΔP1 or the second pressure difference ΔP2 based on the detection result of the pressure difference detector 131.

Consequently, the pressure vessel 103 houses the gasifier 101, the annulus section 104 is defined therebetween, the inside of the gasifier 101 and the annulus section 104 communicate with each other via the pressure equalizing pipes 127, and the pressurizing gas supply device 119 supplies the inert gas to the annulus section 104, whereby the raw syngas is prevented from flowing from the gasifier 101 into the annulus section 104. The pressure difference detector 131 constantly detects the first pressure difference ΔP1 between the first pressure P1 in the gasifier 101 in the reductor 111 and the second pressure P2 in the annulus section 104, and the control device 132 controls the pressurizing gas supply device 119 such that the second pressure P2 is higher than the first pressure P1 based on the detection result of the pressure difference detector 131. More preferably, the pressure difference detector 131 constantly detects the second pressure difference ΔP2 between the third pressure P3 in the gasifier 101 in the pressure equalizing pipes 127 and the fourth pressure P4 in the annulus section 104, and the control device 132 controls the pressurizing gas supply device 119 such that the fourth pressure P4 is higher than the third pressure P3 based on the detection result of the pressure difference detector 131.

The pressurizing gas supply device 119 supplies the inert gas from the gas nozzles 120 so as to be the sum obtained by adding the standard supply amount and the fluctuating supply amount additionally supplied by the pressure rising rate or more. Consequently, even when the first pressure P1 or the third pressure P3 in the gasifier 101 rises, the second pressure P2 or the fourth pressure P4 in the annulus section 104 is appropriately raised more than it, whereby the raw syngas in the gasifier 101 can be prevented from flowing into the annulus section 104 through the pressure equalizing pipes 127.

In the gasification unit of the first embodiment, the pressure equalizing pipes 127 are arranged vertically above the heat exchangers 102 (economizers, superheaters, or evaporators, for example), the first pressure sensor 136 that detects the first pressure P1 in the reductor 111, the second pressure sensor 137 that detects the second pressure P2, and the calculator 138 that calculates the first pressure difference ΔP1 between the first pressure P1 and the second pressure P2 are provided as the pressure difference detector 131, and the control device 132 controls the pressurizing gas supply device 119 such that the first pressure difference ΔP1 is the sum obtained by adding the standard supply amount set by the lower limit value PL with the tolerance added and the fluctuating supply amount that is calculated fro(r) the pressure rising rate of the second pressure P2 and is additionally supplied, consequently, the first pressure difference ΔP1 is determined, whereby the supply amount of the inert gas to the annulus section 104 can be adjusted with high precision even when the pressure fluctuations of the gasifier 101 occur by the load change of the coal gasification unit 12 and the like.

The gasification unit of the first embodiment arranges the first pressure sensor 136 and the second pressure sensor 137 at the same height position and also arranges the third pressure sensor 133 and the fourth pressure sensor 134 at the same height position when they are used. Consequently, even when the density of the raw syngas in the gasifier 101 and the density of the inert gas in the annulus section 104 are different from each other, the first pressure sensor 136 and the second pressure sensor 137, which are arranged at the sane height position, detect the first pressure P1 in the gasifier 101 and the second pressure P2 in the annulus section 104, respectively, and the third pressure sensor 133 and the fourth pressure sensor 134, when being used, detect the third pressure F3 in the gasifier 101 and the fourth pressure F4 in the annulus section 104, respectively, thus the supply amount of the inert gas to the annulus section 104 can be adjusted with high precision with detection errors reduced.

In the gasification unit of the first embodiment, the first pressure sensor 136 that detects the first pressure P1 in the gasifier 101 vertically below the heat exchangers 102 (economizers, superheaters, or evaporators, for example), the second pressure sensor 137 that detects the second pressure P2 in the annulus section 104 below the heat exchangers 102, and the calculator 138 that calculates the first pressure difference ΔP1 between the first pressure P1 and the second pressure P2 are provided as the pressure difference detector 131, and the control device 132 controls the pressurizing gas supply device 119 such that the first pressure difference ΔP1 is the upper limit value PU set based on the furnace wall strength of the gasifier 101 or less. Consequently, when the density of the raw syngas in the gasifier 101 and the density of the inert gas in the annulus section 104 are different from each other, the pressure difference becomes larger toward a lower part, and the upper limit value PU is set based on the furnace wall strength in order to prevent the furnace wall of the gasifier 101 from being damaged. Consequently, the supply amount of the inert gas to the annulus section 104 is adjusted to be the upper limit value or less in accordance with the first pressure difference ΔP1 in a high-temperature region in the lower part of the gasifier 101, whereby the raw syngas can be prevented from flowing into the annulus section 104, and the high integrity of the gasifier 101 can be ensured.

In the gasification unit of the first embodiment, the calculator 135 of the pressure difference detector 131 calculates the estimated value of the first pressure difference ΔP1 in accordance with the load change of the gasifier 101 at start-up or during the load change set in advance, and the control device 132 controls the pressurizing gas supply device 119 such that the first pressure difference ΔP1 is maintained within the certain range set in advance. The fuel flow to be supplied to the gasifier 101 at start-up or during the load change is set in advance, and the first pressure P1 or the third pressure P3 in the gasifier 101 is estimated in accordance with this fuel flow, the estimated value of the first pressure difference ΔP1 or the estimated value of the second pressure difference ΔP2 is estimated and set, and the supply amount of the inert gas with the estimated value being the lower limit value PL or more can be set. Consequently, the supply amount of the inert gas can be set without using the pressure sensors 133 and 134, fluctuations in the supply amount of the inert gas caused by detection errors, detection delays, and the like are prevented, and the supply amount of the inert gas to the annulus section 104 can be adjusted with high precision.

The device and method for controlling the gasification unit of the first embodiment detect the first pressure difference ΔP1 between the first pressure P1 on the gasifier 101 side in the reductor 111 and the second pressure P2 on the annulus section 104 side and control the pressurizing gas supply device 119 such that the second pressure P2 is higher than the first pressure P1 or detect the second pressure difference ΔP2 between the third pressure P3 on the opening 127 a on the gasifier 101 side and the fourth pressure P4 on the opening 127 b on the annulus section 104 side of the pressure equalizing pipes 127 and controls the pressurizing gas supply device 119 such that the fourth pressure P4 is higher than the third pressure P3. Consequently, even when the first pressure P1 or the third pressure P3 in the gasifier 101 rises, the second pressure P2 or the fourth pressure P4 in the annulus section 104 is raised snore than it, whereby the raw syngas in the gasifier 101 can be prevented fro* flowing into the annulus section 104 through the pressure equalizing pipes 127.

The integrated coal gasification combined cycle 10 of the first embodiment includes the coal gasification unit 12 that gasifies coal to generate a combustible gas, the gas purification unit 14 that removes impurities from the combustible gas generated by the coal gasification unit 12 to perform gas purification, the combined cycle power unit 15 that combusts a mixed gas of the combustible gas subjected to the gas purification by the gas purification unit 14 and compressed gas to drive the turbine, the heat recovery steam generator 19 that generates steam by the flue gas from the combined cycle power unit 15, and the steam turbine unit 17 that rotatingly drives the turbine by the steam generated by the heat recovery steam generator 19. Consequently, the raw syngas in the gasifier 101 can be prevented from flowing into the annulus section 104 through the pressure equalizing pipes 127, and facility efficiency can be improved.

Second Embodiment

FIG. 3 is a schematic diagram illustrating a gasification unit of a second embodiment. The members having functions similar to those of the above embodiment are denoted by the same symbols, and detailed descriptions thereof are omitted.

In the second embodiment, as illustrated in FIG. 3, the coal gasification unit 12 constantly controls the supply amount of the inert gas to the annulus section 104 by the pressurizing gas supply device 119 such that the pressure in the annulus section 104 is higher than the pressure in the gasifier 101. In other words, the coal gasification unit 12 is provided with a pressure difference estimation device 141 that estimates the second pressure difference ΔP2 near the pressure equalizing pipes 127 from the first pressure difference ΔP1 between the first pressure P1 in the gasifier 101 and the second pressure P2 in the annulus section 104 and a control device 142 that controls the pressurizing gas supply device 11S such that the second pressure P2 is higher than the first pressure P1 based on an estimation result of the pressure difference estimation device 141.

The pressure difference estimation device 141 has the first pressure sensor 136 that detects the first pressure P1 in the reductor 111 of the gasifier 101 vertically below the heat exchangers 102, the second pressure sensor 137 that detects the second pressure P2 in the annulus section 104 vertically below the neat exchangers 102, and an estimator 143 that estimates the second pressure difference ΔP2 near the pressure equalizing pipes 127 from a detection value of the first pressure sensor, a detection value of the second pressure sensor, and the height position of the pressure equalizing pipes 127. In this case, the first pressure sensor 136 and the second pressure sensor 137 are arranged at the same height position within a range that causes no substantial difference in the measured pressure.

To the estimator 143, the first pressure P1 detected by the first pressure sensor 136 and the second pressure P2 defected by the second pressure sensor 137 are input. The estimator 143 calculates the first pressure difference ΔP1 obtained by subtracting the first pressure P1 from the second pressure P2 and estimates the second pressure difference ΔP2 from the first pressure difference ΔP1 and the height position of the pressure equalizing pipes 127. The density of the raw syngas ascending in the gasifier 101 and the density of the inert gas ascending in the annulus section 104 are different from each other. Consequently, the pressure difference between the gasifier 101 and the annulus section 104 are different from each other in their height positions, that is, in a gas head difference. The density of the raw syngas, the density of the inert gas, the height difference between the opening of the pressure equalizing pipes 127 and the pressure sensors 136 and 137 are determined by design values or experimental values in advance. Consequently, the pressure difference estimation device 141 can estimate the second pressure difference ΔP2 that can control the pressure difference near the pressure equalizing pipes 127 with high precision from the third pressure P3 in the gasifier 101, the fourth pressure P4 in the annulus section 104, and the height difference between the pressure equalizing pipes 127 and the pressure sensors 136 and 137.

The control device 142 compares the second pressure difference ΔP2 estimated by the estimator 143 with the lower limit value PL and the upper limit value PU sot in advance and determines whether the second pressure difference ΔP2 is the lower limit value PL or more and the upper limit value PU or less. The control device 142 controls the pressurizing gas supply device 119 such that the second pressure difference ΔP2 is the lower limit value PL or more and the upper limit value PU or less. In a manner similar to the first embodiment, the pressurizing gas supply device 119 is controlled such that the second pressure difference ΔP2 is the sum obtained by adding the standard supply amount set by the lower limit value PU with the tolerance added and the fluctuating supply amount that is calculated from the pressure rising rate of the fourth pressure P4 and is additionally supplied.

Consequently, in the coal gasification unit 12, owing to pressure fluctuations and the like caused by load changes in the gasifier 101 and the like, the pressure of the raw syngas ascending in this gasifier 101 may be higher than the pressure in the annulus section 104. In this process, in the pressure difference estimation device 141, the first pressure sensor 136 detects the first pressure P1, the second pressure sensor 137 detects the second pressure P2, and the estimator 143 estimates the second pressure difference ΔP2 near the pressure equalizing pipes 127 from the first pressure P1, the second pressure P2, and the height of the pressure equalizing pipes 127. The control device 142 compares the second pressure difference ΔP2 estimated by the estimator 143 with the lower limit value PL and increases the supply amount of the inert gas to be supplied to the annulus section 104 by the pressurizing gas supply device 119 such that the second pressure difference ΔP2 is the lower limit value PL or more. Consequently, even when the pressure in the gasifier 101 increases, the pressure in the annulus section 104 also increases, and the pressure in the gasifier 101 does not exceed the pressure in the annulus section 104.

Subsequently, when the coal gasification unit 12 returns to the rated operation, the pressure in the gasifier 101 drops, and the pressurizing gas supply device 119 is controlled so as to reduce the fluctuating supply amount that is calculated from the pressure rising rate of the fourth pressure P4 and is additionally supplied. However, when the pressure in the gasifier 101 drops fast, the pressure in the annulus section 104 may become significantly higher than the pressure in the gasifier 101. In this process, the control device 142 compares the first pressure difference ΔP1 actually measured with the upper limit value PU and reduces the supply amount of the inert gas to be supplied to the annulus section 104 by the pressurizing gas supply device 119 such that the first pressure difference ΔP1 is the upper limit value PU or less. Consequently, even when the pressure in the gasifier 101 rapidly drops, the pressure in the annulus section 104 also drops, and the differential pressure between the pressure in the gasifier 101 and the pressure in the annulus section 104 does not significantly increase.

Thus, the gasification unit of the second embodiment is provided with the pressure difference estimation device 141 that estimates the second pressure difference ΔP2 near the pressure equalizing pipes 127 from the first pressure difference ΔP1 between the first pressure P1 in the lower part in the vertical direction of the gasifier 101 and the second pressure P2 in the lower part of the annulus section 104 and the control device 142 that controls the pressurizing gas supply device 119 such that the fourth pressure P4 is higher than the third pressure P3 based on the estimation result of the pressure difference estimation device 141. The pressure difference estimation device 141 induces the first pressure sensor 136 that detects the first pressure P1, the second pressure sensor 137 that detects the second pressure P2, and the estimator 143 that estimates the second pressure difference ΔP2 from the first pressure P1, the second pressure P2, and the height position of the pressure equalizing pipes 127.

Consequently, even when the third pressure P3 in the gasifier 101 rises, the fourth pressure P4 in the annulus section 104 is raised more than it, whereby the raw syngas in the gasifier 101 can be prevented from flowing into the annulus section 104 through the pressure equalizing pipes 127. In addition, the pressure sensors 136 and 137 are already provided in order to ensure the integrity of the gasifier 101. Consequently, the estimated values of the first pressure difference ΔP1 and the second pressure difference ΔP2 are determined using the pressure sensors 136 and 137 for maintaining the strength of the gasifier 101 without separately providing any sensor for detecting the pressure near the pressure equalizing pipes 127 in the upper part of the gasifier 101, whereby the supply amount of the inert gas to the annulus section 104 can be appropriately adjusted, and parts costs can be prevented from increasing.

Third Embodiment

FIG. 4 is a schematic diagram illustrating a gasification unit of a third embodiment. The members having functions similar to those of the above embodiment are denoted by the same symbols, and detailed descriptions thereof are omitted.

In the third embodiment, as illustrated in FIG. 4, the coal gasification unit 12 constantly controls the supply amount of the inert gas to the annulus section 104 by the pressurizing gas supply device 119 such that pressure in the annulus section 104 is higher than the pressure in the gasifier 101. In other words, the coal gasification unit 12 is provided with a pressure difference estimation device 151 that estimates the first pressure difference ΔP1 based on the first pressure P1 in the gasifier 101 calculated from a fuel flow to be supplied to the gasifier 101 and a control device 152 that controls the pressurizing gas supply device 119 such that the second pressure P2 is higher than the first pressure P1 based on an estimation result of the pressure difference estimation device 151.

The pressure difference estimation device 151 has a first fuel flow sensor 153 that detects the flow of powdered coal to be supplied to the gasifier 101, a second fuel flow sensor 154 that detects the flow of char to be supplied to the gasifier 101, and an estimator 155 that estimates the first pressure difference ΔP1 from a detection value of the first fuel flow sensor 153 and a detection value of the second fuel flow sensor 154.

To the estimator 155, the flow of the powdered coal detected by the first fuel flow sensor 153 and the flow of the char detected by the second fuel flow sensor 154 are input. The estimator 155 adds the flow of the powdered coal and the flow of the char to calculate a fuel flow, estimates the pressure of the raw syngas in the gasifier 101 based on the fuel flow, and estimates the first pressure difference ΔP1 based on the pressure of the raw syngas in the gasifier 101. The fuel flow and the pressure in the gasifier 101 increase in proportion to each other, and the relation between the fuel flow and the pressure in the pressure in the gasifier 101 is napped. The supply amount of the inert gas to the annulus section 104 is uniquely set as described in the first embodiment. Consequently, the pressure difference estimation device 151 can estimate the first pressure difference ΔP1 from the fuel flow obtained by adding the flow of the powdered coal and the flow of the char.

The control device 152 compares the first pressure difference ΔP1 estimated by the estimator 155 with the lower limit value PL and the upper limit value PU set in advance and determines whether the first pressure difference ΔP1 is the lower limit value PL or more and the upper limit value PU or less. The control device 152 controls the pressurizing gas supply device 119 such that the first pressure difference ΔP1 is the lower limit value PL or mere and the upper limit value PU or less. The specific control of the pressurizing gas supply device 119 by the control device 152 is similar to that of the first and second embodiments, and a description thereof is omitted.

Thus, the coal gasification unit 12 of the third embodiment is provided with the pressure difference estimation device 151 that estimates the first pressure difference ΔP1 based on the first pressure in the gasifier 101 calculated from the fuel flow to be supplied to the gasifier 101 and the control device 152 that controls the pressurizing gas supply device 119 such that the second pressure P2 is higher than the first pressure P1 based on the estimation result of the pressure difference estimation device 151. The pressure difference estimation device 151 includes the first fuel flow sensor 1S3 that detects the flow of the powdered coal to be supplied to the gasifier 101, the second fuel flow sensor 154 that detects the flow of the char to be supplied to the gasifier 101, and the estimator 155 that estimates the first pressure difference ΔP1 from the detection value of the first fuel flow sensor 153 and the detection value of the second fuel flow sensor 154.

Consequently, even when the first pressure P1 in the gasifier 101 rises, the second pressure P2 in the annulus section 104 is raised more than it, whereby the raw syngas in the gasifier 101 can be prevented from flowing into the annulus section 104 through the pressure equalizing pipes 127. In addition, the fuel flow sensors 153 and 154 are already provided in order to measure the fuels flow to the gasifier 101. Consequently, the first pressure difference ΔP1 is determined using the fuel flow sensors 153 and 154 without separately providing any sensor for detecting the pressure near the pressure equalizing pipes 127 in the upper part of the gasifier 101, whereby the supply amount of the inert gas to the annulus section 104 can be appropriately adjusted, and parts costs can be prevented from increasing.

Fourth Embodiment

FIG. 5 is a schematic diagram illustrating a gasification unit of a fourth embodiment. The members having functions similar to those of the above embodiment are denoted by the same symbols, and detailed descriptions thereof are omitted.

In the fourth embodiment, as illustrated in FIG. 5, the coal gasification unit 12 constantly controls the supply amount of the inert gas to the annulus section 104 by the pressurizing gas supply device 119 such that the pressure in the annulus section 104 is higher than the pressure in the gasifier 101. In other words, the coal gasification unit 12 includes a pressure difference estimation device 161 that calculates a furnace pressure rising rate of the gasifier 101 based on the pressure in the gasifier 101 to estimate the first pressure difference ΔP1 and a control device 162 that controls the pressurizing gas supply device 119 such that the second pressure P2 is higher than the first pressure P1 based on an estimation result of the pressure difference estimation device 161.

The pressure difference estimation device 161 has a pressure sensor 163 that detects the pressure in the gasifier 101 and an estimator 164 that estimates the first pressure difference ΔP1 from a detection value of the pressure sensor 163. The pressure sensor 163 detects the pressure in the gasifier 101 at the same height as the height of the opening on the annulus section 104 side of the pressure equalizing pipes 127.

The estimator 164 detects the pressure in the gasifier 101 near the pressure equalizing pipes 127 detected by the pressure sensor 163, calculates the furnace pressure rising rate of the gasifier 101 based on the pressure in the gasifier 101, and estimates the first pressure difference ΔP1 based on this furnace pressure rising rate.

In other words, in many cases, the coal gasification unit 12 is operated to increase the load of the gasifier 101 from its start-up thereby to maintain a stationary load set in advance, and to decrease the load of the gasifier 101 thereby to maintain a load set in advance. In this case, the coal gasification unit 12 increases a fuel flow to be supplied to the gasifier 101, in which a load rising rate at start-up, that is, the degree of increase of the fuel flow is set in advance. In contrast, a load reduction rate, that is, the degree of reduction of the fuel flow nay be set in advance, and thus the operating state of the gasifier 101 can be estimated based on the pressure rising rate cf the gasifier 101, and the pressure situation of a necessary site can be estimated. Consequently, the pressure in the gasifier 101 is detected by the pressure sensor 163, and the estimated value of the first pressure difference ΔP1 or the estimated value of the second pressure difference ΔP2 corresponding to the load change of the gasifier 101 during a load operation set in advance can be estimated and set.

The control device 162 compares the first pressure difference ΔP1 estimated by the estimator 164 with the lower limit value PL and the upper limit value PU set in advance and determines whether the first pressure difference ΔP1 is the lower limit value PL or more and the upper limit value PU or loss. The control device 162 controls the pressurizing gas supply device 119 such that the first pressure difference ΔP1 is the lower limit value PL or more and the upper limit value PU or less. The specific control of the pressurizing gas supply device 119 by the control device 162 is similar to that of the first and second embodiments, and a description thereof is omitted.

Thus, the gasification unit of the fourth embodiment is provided with the pressure difference estimation device 161 that calculates the furnace pressure rising rate of the gasifier 101 based on the pressure in the gasifier 101 to estimate the first pressure difference ΔP1 and the control device 162 that controls the pressurizing gas supply device 119 such that the second pressure P2 is higher than the first pressure P1 based on the estimation result of the pressure difference estimation device 161. The pressure difference estimation device 161 includes the pressure sensor 163 that detects the pressure in the gasifier 101 and the estimator 164 that calculates the furnace pressure rising rate of the gasifier 101 based on the detection value of the pressure sensor 163 to estimate the first pressure difference ΔP1.

Consequently, even when the first pressure P1 in the gasifier 101 rises, the second pressure P2 in the annulus section 104 is raised more than it, whereby the raw syngas in the gasifier 101 can be prevented from flowing into the annulus section 104 through the pressure equalizing pipes 127. In addition, the pressure sensor 163 that detects the pressure in the upper part of the gasifier 101 is provided, consequently, only one sensor for detecting the pressure near the pressure equalizing pipes 127 in the upper part of the gasifier 101 is required, and the first pressure difference ΔP1 is determined using the pressure sensor 163, whereby the supply amount of the inert gas to the annulus section 104 can be appropriately adjusted, and parts costs can be prevented from increasing.

Although the pressure sensors are provided near the pressure equalizing pipes and below the heat exchangers to detect the pressure in the gasifier in the embodiments, the arrangement position is not limited to this height and may be set as appropriate.

In the embodiments, the pressure equalizing pipes are not limited to an L shape; the pressure equalizing pipes may have a cylindrical shape.

Although coal is used as the fuel in the embodiments, a high rank coal or a low rank coal can also be used. Not only coal but biomass used as renewable biologically derived organic resources may be used; thinnings, timber waste, driftwood, herbage, waste, sludge, tires, and recycled materials (pellets and chips) made from them can also be used.

In general, the lower part of the gasifier and the lower part of the annulus section are sealed by hopper water; when the differential pressure between the gasifier and the annulus section increases, the hopper water flows into the gasifier to cut the sealing, whereby the furnace wall strength of the gasifier can be ensured. The present invention does not aim at this point and prevents the raw syngas in the gasifier from flowing into the pressure holding section through the pressure equalising pipes.

Although the present embodiment describes a tower type gasifier, a crossover type gasifier as the gasifier can similarly perform by changing the vertically up-and-down direction of each device to match the gas flow direction of the raw syngas.

REFERENCE SIGNS LIST

10 integrated coal gasification combined cycle (integrated gasification combined cycle)

11 powdered coal supply unit

12 coal gasification unit

13 char recovery unit

14 gas purification unit

15 combined cycle power unit

16 heat recovery steam generator

101 gasifier

102 heat exchanger

103 pressure vessel

104 annulus section (pressure holding section)

119 pressurizing gas supply device

120 gas nozzle

121 gas supply line

122 flow control valve

127 pressure equalizing pipe

131 pressure difference detector (pressure difference detection and estimation device)

132, 142, 152, 162 control device

133 third pressure sensor

134 fourth pressure sensor

135, 138 calculator

136 first pressure sensor

137 second pressure sensor

141, 151, 161 pressure difference estimation device (pressure difference detection and estimation device)

143, 155, 164 estimator

153 first fuel flow sensor

154 second fuel flow sensor

163 pressure sensor 

1. A gasification unit comprising: a gasifier configured to gasify carbonaceous feedstock; a pressure vessel housing the gasifier; a pressure holding section to be filled with a pressurizing gas, the pressure holding section being provided between the gasifier and the pressure vessel; a pressurizing gas supply device configured to supply a pressurizing gas to the pressure holding section; pressure equalizing pipes by which the inside of the gasifier is communicated with the pressure holding section: a pressure difference detection and estimation device configured to detect or estimate a first pressure difference between a first pressure on the gasifier side and a second pressure on the pressure holding section side; and a control device configured to control the pressurizing gas supply device such that the second pressure is higher than the first pressure based on a detection result or an estimation result of the pressure difference detection and estimation device.
 2. The gasification unit according to claim 1, wherein the pressure difference detection and estimation device includes a first pressure sensor provided apart from the pressure equalizing pipes in a gas flow direction to detect the first pressure in the gasifier, a second pressure sensor provided apart from the pressure equalizing pipes in the gas flow direction to detect the second pressure in the pressure holding section, and a calculator configured to calculate the first pressure difference from a detection value of the first pressure sensor and a detection value of the second pressure sensor.
 3. The gasification unit according to claim 1, wherein the pressure difference detection and estimation device detects or estimates a second pressure difference between a thud pressure on an opening of the pressure equalizing pipe on the gasifier side and a fourth pressure on an opening of the pressure equalizing pipe on the pressure holding section side, and the control device controls the pressurizing gas supply device such that the fourth pressure is higher than the thud pressure based on a detection result or an estimation result of the pressure difference detection and estimation device.
 4. The gasification unit according to claim 3, comprising a heat exchanger arranged in a vertically upper part of the gasifier, wherein the pressure equalizing pipes are arranged vertically above the heat exchanger, the pressure difference detection and estimation device includes a third pressure sensor configured to detect the third pressure, a fourth pressure sensor configured to detect the fourth pressure, and a calculator configured to calculate the second pressure difference from a detection value of the third pressure sensor and a detection value of the fourth pressure sensor, and the control device controls the pressurizing gas supply device such that the second pressure difference is a lower limit value with a tolerance set in advance added or more.
 5. The gasification unit according to claim 4, wherein the third pressure sensor and the fourth pressure sensor are arranged at a same height position.
 6. The gasification unit according to claim 1, wherein a supply amount of the pressurizing gas is controlled as the sum of a standard supply amount and a fluctuating supply amount, the standard supply amount being set such that the first pressure difference is a certain pressure difference or more, the certain pressure difference providing a pressure difference at a normal situation during normal rated operation, and the control device calculates the fluctuating supply amount to be additionally supplied at a pressure rising rate of the second pressure detected by the second pressure sensor in the pressure holding section.
 7. The gasification unit according to claim 1, wherein a supply position of the pressurizing gas to the pressure holding section by the pressurizing gas supply device is a position apart from the pressure equalizing pipes vertically downward by a certain distance.
 8. The gasification unit according to claim 1, wherein the pressure difference detection and estimation device includes a first pressure sensor provided apart from the pressure equalizing pipes in a gas flow direction to detect a first pressure in the gasifier, a second pressure sensor provided apart from the pressure equalizing pipes in the gas flow direction to detect a second pressure in the pressure holding section, and a calculator configured to calculate a second pressure difference from a detection value of the first pressure sensor and a detection value of the second pressure sensor, and the control deuce controls the pressurizing gas supply device such that the second pressure difference is an upper limit value set based on a furnace wall strength of the gasifier or less.
 9. The gasification unit according to claim 3, wherein the pressure difference detection and estimation device includes a first pressure sensor configured to detect a first pressure, a second pressure sensor configured to detect a second pressure in a lower part of the pressure holding section, and an estimator configured to estimate the second pressure difference from a detection value of the first pressure sensor, a detection value of the second pressure sensor, and a height position of the pressure equalizing pipes, and the control device controls the pressurizing gas supply device such that the second pressure difference is maintained within a certain range set in advance.
 10. The gasification unit according to claim 1, wherein the pressure difference detection and estimation device includes a fuel flow sensor configured to detect a fuel flow to be supplied to the gasifier and an estimator configured to estimate a pressure in the gasifier based on a detection value of the fuel flow sensor to estimate the first pressure difference, and the control device controls the pressurizing gas supply device such that the first pressure difference is maintained within a certain range set in advance.
 11. The gasification unit according to claim 1, wherein the pressure difference detection and estimation device includes a pressure sensor configured lo detect a pressure in the gasifier and an estimator configured to calculate a furnace pressure rising rate of the gasifier based on a detection value of the pressure sensor to estimate the first pressure difference, and the control device controls the pressurizing gas supply device such that the first pressure difference is maintained within a certain range set in advance.
 12. The gasification unit according to claim 1, wherein the pressure difference detection and estimation device includes a calculator configured to calculate the first pressure difference in accordance with a load change of the gasifier at start-up set m advance, and the control device controls the pressurizing gas supply device such that the first pressure difference is maintained within a certain range set in advance.
 13. A control device for a gasification unit that includes a gasifier configured to gasify a carbon-containing fuel, a pressure vessel housing the gasifier, a pressure holding section to be filled with a pressurizing gas, the pressure holding section being provided between the gasifier and the pressure vessel, a pressurizing gas supply device configured to supply a pressurizing gas to the pressure holding section, and pressure equalizing pipes by which the inside of the gasifier is communicated with the pressure holding section, the control device controlling the pressurizing gas supply device such that a second pressure on the pressure holding section side is higher than a first pressure on the gasifier side.
 14. A control method for a gasification unit that includes a gasifier configured to gasify a carbon-containing fuel, a pressure vessel housing the gasifier, a pressure holding section to be filled with a pressurizing gas, the pressure holding section being provided between the gasifier and the pressure vessel, a pressurizing gas supply device configured to supply a pressurizing gas to the pressure holding section, and pressure equalizing pipes by which the inside of the gasifier is communicated with the pressure holding section, the control method comprising: detecting or estimating a first pressure difference between a first pressure on the gasifier side and a second pressure on the pressure holding section side; and controlling the pressurizing gas supply device such that the second pressure is higher than the first pressure.
 15. An integrated gasification combined cycle comprising: the gasification unit according to claim 1 configured to gasify carbonaceous feedstock to generate a combustible gas; a gas purification unit configured to remove impurities from the combustible gas generated by the gasification unit to perform gas purification; a gas turbine unit configured to combust a mixed gas of at least part of the combustible gas subjected to gas purification by the gas purification unit and compressed air to rotatingly drive a turbine; a heat recovery steam generator configured to generate steam by a flue gas from the gas turbine unit; and a steam turbine unit configured to rotatingly drive a turbine by the steam generated by the heat recovers steam generator. 